Remote Sensing of High Temperatures with Refractory, Direct-Contact Optical Metacavity

In this work, temperature-dependent optical properties of refractory plasmonic transition metal nitrides and dielectric thin films are utilized to design and realize a planar, direct-contact, nanophotonic metacavity for remote, all-optical sensing of a wide range of surface temperatures (from room temperature to above 1000 °C). The proposed hybrid metacavity device integrates the plasmonic cavity with a planar metasurface that utilizes refractory material components, namely, titanium nitride (TiN) and silicon nitride (Si₃N₄), and operates in a spectral wavelength window of 900–1400 nm. The unique feature of this approach is that metacativy is located directly on the hot surface, while other components are kept remote. The thermally variant optical properties of the constituent materials (TiN, Si₃N₄) enable metacavity operation with a strong polarization-dependent resonant reflectance response. At the cavity resonance, relative amplitude variations of above 30% are detected in the temperature-dependent reflectance spectra that act as the read-out from the experimentally demonstrated sensor. The proposed high-efficiency, planar optical refractory sensor located directly on hot surfaces also allows for great scalability. The device enables true remote all-optical measurements by keeping other ancillary systems outside of the hot ambient conditions and, therefore, is especially relevant for applications in harsh environments.